Adds shares, comments from conference call and details in paragraphs 1,6,7,10,11

By Pooja Menon

May 6 (Reuters) - Power producer NRG Energy NRG.N on Wednesday missed Wall Street estimates for first-quarter adjusted profit, hurt by milder weather in Texas and increased costs, sending its shares down 3.6% in early trading.

The company's interest expenses in the quarter rose to $285 million from $163 million a year ago, impacted by costs related to the completed acquisition of power generation assets from investment firm LS Power in a deal valued at $12 billion.

Houston, Texas-based NRG's operating costs were up 33.4% to $9.93 billion.

The company expects commercial operations at the 415-megawatt T.H. Wharton facility in Texas, its first project, to begin by the end of May.

Within its existing fleet, NRG sees up to 2 gigawatts of uprate and commercial conversion opportunities, up from nearly 1 gigawatt previously disclosed, company executives said during a conference call.

The incremental gigawatt would come from traditional natural gas upgrades, in addition to the previously disclosed CT‑to‑CCGT (combustion turbine to combined‑cycle gas turbine) conversion potential.

Separately, insider Robert Gaudette last week succeeded Larry Coben as the company's CEO.

NRG posted quarterly revenue of $10.26 billion, up from $8.59 billion a year ago.

Adjusted core profit at its Texas unit fell 27.8% to $216 million amid mild winter weather that saw a nearly 30% decrease in heating degree days leading to lower retail load.

Earlier this year, power plant outages surged along the eastern U.S. as constricted natural gas supplies and frigid temperatures cut the electricity output of the region's generation fleet.

As a result, adjusted EBITDA at the company's East segment fell 2% to $464 million, due to higher power supply costs during Winter Storm Fern.

Adjusted profit of $1.49 per share for the three months ended March 31 fell short of analysts' average estimate of $1.78, according to data compiled by LSEG.